Refrigeration apparatuses operable to perform a refrigeration cycle are well known in the conventional technology. Such a type of refrigeration apparatus has a variety of applications, for example, in the field of air conditioners. Patent Document I discloses a refrigeration apparatus of the type which includes an expander. In the refrigeration apparatus disclosed in Patent Document I, the expander is connected, through a single shaft, to a compressor. In the refrigeration apparatus of Patent Document I, high pressure refrigerant after heat dissipation is expanded in the expander for the recovery of power. The power recovered in the expander is used to drive the compressor, with a view to achieving improvement in the coefficient of performance (COP).
In a typical refrigeration apparatus, refrigerant is circulated in a refrigerant circuit configured in the form of a closed circuit. This produces the necessity of constantly keeping the mass flow rate of refrigerant through the expander and the mass flow rate of refrigerant through the compressor at the same value. However, the refrigeration apparatus, when in operation, undergoes variations in the operating condition (e.g., the variation in the high pressure of the refrigeration cycle and the variation in the low pressure of the refrigeration cycle). In consequence, the density of refrigerant that flows into the compressor and the compressor will vary. If, like Patent Document I, the expander is coupled to the compressor by a single shaft, the rotation speed of the expander and the rotation speed of the compressor constantly become equal. Therefore, if both the expander and the compressor are implemented by positive displacement fluid machines, this results in occurrence of an imbalance between the mass flow rate of refrigerant through the expander and the mass flow rate of refrigerant through the compressor. This might make it impossible for the refrigeration apparatus to continuously perform a stable refrigerant cycle.
On the other hand, in the refrigeration apparatus of Patent Document I, a bypass passageway is provided in parallel with the expander and a flow rate control valve is arranged along the bypass passageway. When the mass flow rate of refrigerant passable through the expander becomes excessively small relative to the mass flow rate of refrigerant through the compressor, the refrigerant is made to flow through both the expander and the bypass passageway.
Patent Document I: JP 2001-116371A